If you use a windy gun (air or lecky) you shouldn't need to lock the crank, at least I haven't on the three I have done with my cheapo Clarke 240V gun. Regarding the cam locking tool I only use it to hold the pulleys while I loosen or tighten the bolts as it is only a hindrance when refitting the belt.
The flywheel locking pin is for holding the crank in the correct place for doing the belt. It's not designed to take the torque of releasing the pulley bolt.
It's important that the pin is used when fitting the belts though. A 6mm twist drill is all that's needed to do the job with sufficient accuracy